Born and raised in Hong Kong, Brannan studied for a master’s degree at Durham University in England and in 2017 submitted her thesis on how individual grey seals differ in their response to stress.

She returned to Hong Kong and joined Sea Mammal Research Unit Consulting. Today’s outing is a survey focused on one of Hong Kong’s largest and yet least known animals: the Indo-Pacific finless porpoise.

Three times in recent weeks Brannan has been on porpoise surveys; three times she has returned to shore without glimpsing a single one. Suddenly, her calm demeanour is gone. “Porpoise!” she shouts. “There, in front of the boat.”

Before the rest of us can redirect our gazes, the mammal is underwater again. Nevertheless, its brief appearance has delighted Brannan.

“There was a little blow [of water from its blowhole], two or three times, really close,” she says. She suddenly spots another and adds, as if there might be any doubt about her excitement: “That’s made my week.”

It might seem odd, being thrilled at the brief sight of a creature that resembles a dark grey inner tube bobbing briefly to the surface, but this porpoise is one of only two species of porpoises that lack a dorsal fin.

Although the mammal looks nothing special when surfacing – and it doesn’t leap from the water as dolphins do – photos of finless porpoises in captivity show they have faces with an almost cartoonlike cuteness. Their heads are rounded, with widely spaced, prominent black eyes, and upturned mouths suggesting they are perpetually smiling.

Indo-Pacific finless porpoises inhabit tropical coastal waters ranging from the Arabian Sea to southern China. While their total population is unknown, they are in no way abundant, and face threats including being trapped and drowned in fishing nets. This has led to the species being classed as vulnerable on the International Union for Conservation of Nature’s Red List of Threatened Species.

In Hong Kong, they face another possible threat: construction of a huge waste disposal incinerator and related land reclamation on one of the islands in waters they inhabit in the South China Sea.

The most reliable estimate of the porpoise population in waters around Hong Kong and neighbouring Guangdong province – based on surveys conducted around the turn of the century – suggests they may number about 200.

Growing to just 1.8 metres (five feet 11 inches) in length, according to the Hong Kong Dolphin Conservation Society, the finless porpoise is smaller than its more familiar local cousin, the Chinese white dolphin, which can grow up to 2.7 metres long. While the dolphin favours estuarine waters in the mouth of the Pearl River Delta, the porpoise is more of a marine creature, and the only place the two species could be seen together is around the Soko Islands, off southwestern Lantau Island.

Between 1995 and early 2018, Hong Kong’s Agriculture, Fisheries and Conservation Department supported surveys by local marine mammal expert Samuel Hung Ka-yiu and colleagues, which found that porpoises mostly inhabited the waters from the Sokos to southern Cheung Chau island.

Perhaps unsurprisingly, they largely avoid routes plied by high-speed vessels that cross the delta’s mouth between Hong Kong and the gambling mecca of Macau. Instead they favour quieter places, such as the waters off southwest Shek Kwu Chau – which is the site chosen for the planned waste incinerator, dubbed officially by the Hong Kong government as an “integrated waste management facility”.

An artificial island is planned for the incinerator, and given that this could affect the finless porpoises, the contractor – a joint venture between Keppel Seghers and Zhen Hua – has commissioned surveys to assess how they respond while work proceeds. These include today’s outing by the Sea Mammal Research Unit team.

Rather than randomly roaming the sea, the researchers follow a set pattern. They use GPS measurements to determine the start and end points of eight north-south transects in which porpoises should be visible, each about two kilometres (1.2 miles) long. The first of these begins perhaps a kilometre east of the Sokos, and the porpoise sighting that so thrilled Brannan was towards the end of the fourth transect, in open water several hundred metres southwest of Shek Kwu Chau.

We don’t agree there will be no significant impact on finless porpoises from the construction of the incinerator

Taison Chang Ka-tai, chairman, Hong Kong Dolphin Conservation Society

Porpoises use echolocation to find their food, including fish, shrimp and squid, emitting a stream of clicks above the range of human hearing. To help detect them, the team is towing a hydrophone behind the boat, and research technician Arthur Lee sits at a table in the boat’s cabin, wearing headphones to monitor sound modulated so it can be heard by the human ear. “I heard them clearly,” he reports via walkie-talkie.

Another transect takes the boat past the future incinerator site, where work is under way on early stages of the reclamation. A couple of barges are equipped with rigs and booms; another appears specialised for driving piles into the seabed. A moored dredger is loaded with sand.

There is no surprise when there is neither sight nor sound of porpoises here. Yet this used to be one of their favoured locales. During “baseline monitoring” from January 30 to May 14 last year – which overlapped with preparations for the reclamation work – finless porpoises were frequently sighted in the area until the second week of March, when boats and construction platforms arrived to begin seabed assessments. Afterwards, the mammals appeared to have deserted the area.

An environmental impact assessment on the proposed site of the incinerator anticipated that the porpoises would be disturbed if the work went ahead, but confidently predicted mitigation measures would keep any adverse impacts to an “acceptable level”.

This is not a view shared by conservationists including Taison Chang Ka-tai, chairman of the Hong Kong Dolphin Conservation Society, who says in an email: “We don’t agree there will be no significant impact on finless porpoises from the construction of the incinerator.”

Chang adds that the huge impact during the ground investigation work “shows that the real construction process will have a larger impact on finless porpoises when there are more working vessels and noise. Shek Kwu Chau is proven to be a critical habitat in Hong Kong waters for finless porpoises.” He also says that issues such as marine traffic routes pose an additional threat to the porpoises.

The main mitigation measure proposed is the creation of a Southwest Lantau Marine Park, to encompass waters west of Shek Kwu Chau and around the Soko Islands. However, work on establishing this has been slow, due in part to objections from some nearby villagers.

Experience with the Chinese white dolphin reveals marine parks are no magical panacea for disturbance from development. Two such parks were established for the dolphins north of Lantau. Yet during work on the Hong Kong-Zhuhai-Macau Bridge, dolphin numbers plummeted, and individuals moved southwest, leaving these supposed sanctuaries almost bereft of the marine creatures.

Last year, 33 dead finless porpoises were logged by Hong Kong’s Ocean Park Conservation Foundation, equal to the previous record high set in 2014, and representing 12 per cent of the tally since the foundation started investigating stranded dolphins and porpoises in May 2006.

As yet, it is too early to tell if there has been an uptick in deaths due to the reclamation work. “We will need to keep an eye on the number in the following years,” Chang says.

South of Cheung Chau, the boat turns to start another transect, and again there’s a shout of “Porpoise!” This time I just about see one – a steely grey shape that bobs up amid the waves, and is then lost from view again. There are a couple more transects after this, between Shek Kwu Chau and Cheung Chau, but there is not even a hint of a porpoise.

A morning’s work has yielded four porpoise sightings; rewarding for Brannan and the team, yet a paltry figure. More may arrive in coming weeks, as previous surveys indicate that finless porpoises migrate here – from somewhere unknown – possibly because squid numbers are set to increase in early spring.